This invention relates to a low load floor motor vehicle and more particularly a low load floor vehicle that has a longitudinally mounted front engine and a rear wheel drive. This low load floor vehicle has special application as a medium duty bus and delivery truck.
The advantages of having a passenger or cargo vehicle with a flat load floor are well known. Heavy-duty trucks usually have longitudinally mounted front engines and rear drives. A flat load floor is obtained with such vehicles by raising the load floor to a sufficient height to clear all obstructions beneath the load floor. The load floor height can be approximately about four feet. Heavy-duty busses obtain a somewhat lower flat floor area in the forward part of the bus by providing a transversely mounted rear engine that drives rear wheels. The complexities of such a drive make it expensive. As to smaller vehicles, such as medium duty trucks and busses, it is desirable to have a low load floor, as well as a flat load floor. A low step height into the vehicle makes the vehicle much more accessible for loading both passengers and cargo. However, in smaller vehicles, including medium duty busses and trucks, a rear engine/rear drive power package is not a commercially viable option.
It is well known that one can obtain a low flat load floor in a vehicle by disposing the vehicle engine and power train wholly in the front of the vehicle. Such vehicles are already commercially available. Such a vehicle can provide a low step height to the load floor that makes the vehicle much more accessible for loading both passengers and cargo. However, the utility of such vehicles is limited because the driving wheels are not located under the part of the vehicle carrying the load. Improved weight balance and load-carrying capacity is achieved if the engine is in the front of the vehicle and the driving wheels are in the back of the vehicle, under the load.
Because of low load floor front drive trucks and busses have practical limitations, there is still interest in finding an economical rear drive truck and bus that has a low load floor. In addition, disposing the vehicle engine in the front of the vehicle leaves the back of the vehicle more available for passengers and/or cargo. Further, it should be understood that extensive worldwide manufacture and sales of front-engine/rear drive trucks and buses has provided a vast engineering and use experience with front engine/rear drive power trains. This vast experience has provided lowest cost and highest durability for such power trains. For these and other reasons, there is continued manufacture and use of front-engine/rear drive trucks and buses, even though their load floors are relatively high. Because of this extensive production and use experience, there continues to be interest in utilizing front engine/rear drive power trains for low profile and/or low load floor vehicles. However, until my design innovation, no commercially practical design for such a vehicle has been discovered.
It would be of considerable commercial advantage if a low and flat load floor vehicle could be made using mostly traditional front engine/rear drive components. If so, the traditional components would be useful in the manufacture of both the traditional and the low profile vehicles. It would be of even greater advantage if the low load floor vehicle and the traditional vehicle were generally the same forward of the load floor. This will tend to reduce development costs of the low profile vehicle, and make it manufactureable at lower cost and higher durability. I have discovered how to attain this goal. My discovery is particularly of interest to medium duty trucks and busses, where rear drive is quite important.
It is an object of the present invention to provide a low load floor vehicle having a front engine and a rear drive.
It is another object of the invention to provide an improved power train that enables lower cost manufacture of a low profile vehicle having a rear drive.
It is a further object of this invention to provide a step-down transfer case for transmitting front engine power to rear wheels.
One aspect of the present invention contemplates a vehicle having a conventional in-line front engine, a conventional transmission, a step down power transfer case on the rear of the transmission, and a conventional drive shaft extending towards the vehicle rear. The drive shaft extends to a frame-mounted differential that has opposed half-shaft axles, sometimes referred to simply as half-shafts, extending to rear wheels on opposite sides of the vehicle. The step down transfer case is belt, chain or gear driven and differs from a four-wheel drive transfer case in providing a rear output at a level closer to the roadway 35. The drive shaft can now even be lower in the front than the rear, and preferably is not segmented. The lowered rear output of the step down transfer case and a fixed location of the differential allows the load floor of the vehicle to be very low and flat between the step down transfer case and the differential. If the load floor is very low, there may have to be a step up in the load floor at the differential area to accommodate the differential and the suspension system. However, it can still be flat from the step all the way to the rear.
Lowest load floors are attained by also using a low profile rear suspension system, but especially by also using geared wheel drives on the out board ends of the half-shaft axles. The geared wheel drives split the final drive ratio with the differential, to allow use of a smaller diameter ring gear in the differential. The result is that the differential is smaller, which allows a lower load floor over the differential.
Low load floors all the way to the back of the vehicle can be achieved. However, in many instances a small step up in the differential area may be desired for disposition of non-power train components and accessories under the load floor. A small step up may also be desired if there is rear overhang of the load floor. An appropriate step up supplies rear ground clearance, to enable the vehicle to enter inclines without having its rear strike the roadway.
In a special embodiment of the present invention, a special low profile trailing arm suspension system is used for the rear wheels that allows use of air springs. The air springs can be deflated when the vehicle is parked, to lower rear load floor height. Hence, the rear of the vehicle is made more accessible.
It is currently preferred to interpose my step down transfer case as an adapter module between a conventional manual or automatic transmission and a drive shaft. However, it is recognized that in due course, it may be desirable to integrate the step down feature of my transfer case with the transmission.
In yet other aspects of the present invention, if excessively long, the drive shaft might be supported with an intermediate bearing block. While not preferred, the drive shaft could be segmented by an intermediate universal joint.